In recent years, the amount of data handled at information terminals and on the Internet and clouds has been increasing explosively. The explosive increase has led to demands for an increase in the capacity of memory devices and a reduction in bit cost.
Ideal memory devices are nonvolatile semiconductor memory which is high in operating speed and storage density and which is low in bit cost. At present, no memory device meeting all these demands is present, and memory devices suitable for individual intended purposes are provided to users.